The present invention pertains to improvements of chopping apparatus for cutting fiber and strands of material such as mineral fiber including fiber glass, synthetic fibers including polyester or polyethylene and natural fibers including hemp and cotton, or for cutting ribbon like materials, and the method of using the improved chopper to make chopped products at high speeds of several thousand feet per minute. The apparatus is a vast improvement over the choppers used heretofore in that the improved chopper of the present invention greatly reduces and essentially eliminates stringers and fuzz in the chopped strand product and also reduces chopped fiber losses.
Chopped fiber and chopped strands are used in a number of different processes to make many useful products. They are mixed with many kinds of plastics and molded into a wide variety of parts and articles such as automotive parts and building parts. Chopped fiber and chopped strands are also made into dilute aqueous slurries and formed into nonwoven mats used to make roofing, flooring and automotive products and parts.
In processes of making chopped fiber of various kinds, a chopper receives continuously one or more strands made up of a plurality of fibers and chops the strand(s) into short lengths generally ranging from about xe2x85x9 th inch to 3 or more inches long. The strand(s) are often moving very fast through the chopper, typically at several thousand feet per minute. One example of such a process is the process of making chopped glass fiber as disclosed in U.S. Pat. Nos. 3,508,461, 3,771,701, 3,815,461, 3,869,268, 4,175,939, 4,249,441, 4,347,071, 4,373,650, 4,398,934, 4,411,180, 4,551,160, 4,576,621,and 4,840,755, the disclosures of which are herein incorporated by reference.
Prior art choppers occasionally fail to cut completely all the strands passing through the chopper resulting in xe2x80x9cstringersxe2x80x9d, fibers and strands of fiber that vary in length from a few inches to several feet. Also, fibers break and build up fuzz on parts of the prior art choppers and periodically break loose in clumps and go into the chopped product. A clump of fuzz is a tangled mass of one or more long fibers and since it won""t disperse completely in the customers processes, most fuzz clumps may cause defects in the final products. The industry has tried for a long time to eliminate the stringer and fuzz problems and while the frequency has been reduced, at least at times, the problems remain serious and costly. Stringers and fuzz clumps, if present in the chopped strand cause costly defects in the products in which the chopped fiber and chopped strand are used.
Another problem with the prior art choppers is that they throw a very small percentage of good chopped fiber onto the chopper frame or onto the floor causing a housekeeping problem and reducing the material efficiency of the process. Attempts have been made to correct this problem with little or no success.
A chopper assembly for which the improvements of the present invention apply includes a blade roll, a backup roll and a drive. The chopper assembly can also include an optional idler or puller roll for holding the fiber strands against the outer surface of the backup roll to keep the strands from slipping on the backup roll and reducing the pulling speed of the strands and causing undesirable fiber diameters and chopped lengths. The idler roll normally extends beyond the outer edge of the backup roll. The chopper assembly can also include an optional new strand starting system which includes a first starter roll or shoe, a starter bar, a second starting roll or shoe and an accelerating roll. A shoe is a U or V grooved roll or roll segment or a roll flanged on one end that either doesn""t rotate, or if it does, at a very low surface speed or a roll that turns with a minimum resistance producing a surface speed similar to the moving strand in contact with the shoe. The shoes are typically made of low friction, long wearing materials like graphite, bronze or high density epoxy resin impregnated linen fabric composites like Micarta(trademark).
The causes for the stringer and fuzz problems getting into the chopped strand products have now been discovered and solutions to these problems described above have now been developed. When fiberizing molten glass into fibers continuously from a heated precious metal bushing, a well known process, fibers break frequently just below the bushing. When one fiber breaks, very soon the rest of the fibers break and this creates a loose tail on the strand that is then pulled toward the chopper. It has now been discovered that these loose tails often do not get cut completely and end up in the product as stringers of various lengths from a few inches to several feet. It has also been discovered that the fuzz clumps are caused by one or more fibers being broken by a start up shoe and by sharp or rough edges of the protective guard covering the main working parts of the chopper.
The present invention includes a strand guide mounted upstream of the chopper and upstream from a strand separator roll or grooved oscillating roll as is well known, but down stream from a vertical projection of the closest fiberizer. This strand guide prevents the loose tail, from swinging such that it would cause the strand to be thrown out of the strand separator roll and be pulled out of the nip between the blade roll and the back up roll or the chopper. The present invention also includes an improved starter shoe mounted on an air bearing and having a controlled rate of revolution (controlled resistance to rotation) which eliminates fiber breakage on the shoe and puts some tension into a new strand being started into the chopper to cause the strands to stay in the proper strand path.
The present invention also includes a new improved mount for an idler roll of the prior art choppers which allows for easy and fast removal and replacement of an idler roll assembly. This inventive mount, because of its improved structural integrity and integration of the components, also keeps the surface of the idler roll in better contact with the strands running on the back up roll and thus keeps the strands in the nip between the blade roll and the back up roll. The present invention also includes a strand guide insert for the protective cover guard for the working parts of the chopper which prevents the fibers from breaking and causing fuzz when a strand strikes an edge in an opening in the cover guard.
It has also been discovered that most of the good chopped strands thrown onto the floor of the fiber forming room by the chopper occurs because some chopped strands hang onto the peripheral surface of the backup roll for a fraction of a second and are then thrown off. The present invention also includes a deflector plate mounted in such a place that an edge of a deflector plate is kept very close to the peripheral surface of the back up roll and such that any chopped strands striking a working surface of the deflector plate will fall off into the flow of product. The deflector plate is preferably mounted in such a way that the top edge can be adjusted with respect to the peripheral surface of the backup roll while the chopper is operating.